[PATCH 1/2] selinux: revert "stop passing MAY_NOT_BLOCK to the AVC upon follow_link"

[PATCH 1/2] selinux: revert "stop passing MAY_NOT_BLOCK to the AVC upon follow_link"

[Stephen Smalley]

This reverts commit e46e01eebbbc ("selinux: stop passing MAY_NOT_BLOCK
to the AVC upon follow_link"). The correct fix is to instead fall
back to ref-walk if audit is required irrespective of the specific
audit data type.  This is done in the next commit.

Fixes: e46e01eebbbc ("selinux: stop passing MAY_NOT_BLOCK to the AVC upon follow_link")
Reported-by: Will Deacon <will@kernel.org>
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
---
 security/selinux/avc.c         | 24 ++++++++++++++++++++++--
 security/selinux/hooks.c       |  5 +++--
 security/selinux/include/avc.h |  5 +++++
 3 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/security/selinux/avc.c b/security/selinux/avc.c
index ecd3829996aa..74c43ebe34bb 100644
--- a/security/selinux/avc.c
+++ b/security/selinux/avc.c
@@ -862,8 +862,9 @@ static int avc_update_node(struct selinux_avc *avc,
 	 * permissive mode that only appear when in enforcing mode.
 	 *
 	 * See the corresponding handling in slow_avc_audit(), and the
-	 * logic in selinux_inode_permission for the MAY_NOT_BLOCK flag,
-	 * which is transliterated into AVC_NONBLOCKING.
+	 * logic in selinux_inode_follow_link and selinux_inode_permission
+	 * for the VFS MAY_NOT_BLOCK flag, which is transliterated into
+	 * AVC_NONBLOCKING for avc_has_perm_noaudit().
 	 */
 	if (flags & AVC_NONBLOCKING)
 		return 0;
@@ -1205,6 +1206,25 @@ int avc_has_perm(struct selinux_state *state, u32 ssid, u32 tsid, u16 tclass,
 	return rc;
 }
 
+int avc_has_perm_flags(struct selinux_state *state,
+		       u32 ssid, u32 tsid, u16 tclass, u32 requested,
+		       struct common_audit_data *auditdata,
+		       int flags)
+{
+	struct av_decision avd;
+	int rc, rc2;
+
+	rc = avc_has_perm_noaudit(state, ssid, tsid, tclass, requested,
+				  (flags & MAY_NOT_BLOCK) ? AVC_NONBLOCKING : 0,
+				  &avd);
+
+	rc2 = avc_audit(state, ssid, tsid, tclass, requested, &avd, rc,
+			auditdata, flags);
+	if (rc2)
+		return rc2;
+	return rc;
+}
+
 u32 avc_policy_seqno(struct selinux_state *state)
 {
 	return state->avc->avc_cache.latest_notif;
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 36e531b91df2..3eaa3b419463 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3008,8 +3008,9 @@ static int selinux_inode_follow_link(struct dentry *dentry, struct inode *inode,
 	if (IS_ERR(isec))
 		return PTR_ERR(isec);
 
-	return avc_has_perm(&selinux_state,
-			    sid, isec->sid, isec->sclass, FILE__READ, &ad);
+	return avc_has_perm_flags(&selinux_state,
+				  sid, isec->sid, isec->sclass, FILE__READ, &ad,
+				  rcu ? MAY_NOT_BLOCK : 0);
 }
 
 static noinline int audit_inode_permission(struct inode *inode,
diff --git a/security/selinux/include/avc.h b/security/selinux/include/avc.h
index 7be0e1e90e8b..74ea50977c20 100644
--- a/security/selinux/include/avc.h
+++ b/security/selinux/include/avc.h
@@ -153,6 +153,11 @@ int avc_has_perm(struct selinux_state *state,
 		 u32 ssid, u32 tsid,
 		 u16 tclass, u32 requested,
 		 struct common_audit_data *auditdata);
+int avc_has_perm_flags(struct selinux_state *state,
+		       u32 ssid, u32 tsid,
+		       u16 tclass, u32 requested,
+		       struct common_audit_data *auditdata,
+		       int flags);
 
 int avc_has_extended_perms(struct selinux_state *state,
 			   u32 ssid, u32 tsid, u16 tclass, u32 requested,
-- 
2.23.0

[PATCH 2/2] selinux: fall back to ref-walk if audit is required

[Stephen Smalley]

commit bda0be7ad994 ("security: make inode_follow_link RCU-walk aware")
passed down the rcu flag to the SELinux AVC, but failed to adjust the
test in slow_avc_audit() to also return -ECHILD on LSM_AUDIT_DATA_DENTRY.
Previously, we only returned -ECHILD if generating an audit record with
LSM_AUDIT_DATA_INODE since this was only relevant from inode_permission.
Move the handling of MAY_NOT_BLOCK to avc_audit() and its inlined
equivalent in selinux_inode_permission() immediately after we determine
that audit is required, and always fall back to ref-walk in this case.

Fixes: bda0be7ad994 ("security: make inode_follow_link RCU-walk aware")
Reported-by: Will Deacon <will@kernel.org>
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
---
 security/selinux/avc.c         | 24 +++++-------------------
 security/selinux/hooks.c       | 11 +++++++----
 security/selinux/include/avc.h |  8 +++++---
 3 files changed, 17 insertions(+), 26 deletions(-)

diff --git a/security/selinux/avc.c b/security/selinux/avc.c
index 74c43ebe34bb..23dc888ae305 100644
--- a/security/selinux/avc.c
+++ b/security/selinux/avc.c
@@ -424,7 +424,7 @@ static inline int avc_xperms_audit(struct selinux_state *state,
 	if (likely(!audited))
 		return 0;
 	return slow_avc_audit(state, ssid, tsid, tclass, requested,
-			audited, denied, result, ad, 0);
+			audited, denied, result, ad);
 }
 
 static void avc_node_free(struct rcu_head *rhead)
@@ -758,8 +758,7 @@ static void avc_audit_post_callback(struct audit_buffer *ab, void *a)
 noinline int slow_avc_audit(struct selinux_state *state,
 			    u32 ssid, u32 tsid, u16 tclass,
 			    u32 requested, u32 audited, u32 denied, int result,
-			    struct common_audit_data *a,
-			    unsigned int flags)
+			    struct common_audit_data *a)
 {
 	struct common_audit_data stack_data;
 	struct selinux_audit_data sad;
@@ -772,17 +771,6 @@ noinline int slow_avc_audit(struct selinux_state *state,
 		a->type = LSM_AUDIT_DATA_NONE;
 	}
 
-	/*
-	 * When in a RCU walk do the audit on the RCU retry.  This is because
-	 * the collection of the dname in an inode audit message is not RCU
-	 * safe.  Note this may drop some audits when the situation changes
-	 * during retry. However this is logically just as if the operation
-	 * happened a little later.
-	 */
-	if ((a->type == LSM_AUDIT_DATA_INODE) &&
-	    (flags & MAY_NOT_BLOCK))
-		return -ECHILD;
-
 	sad.tclass = tclass;
 	sad.requested = requested;
 	sad.ssid = ssid;
@@ -855,16 +843,14 @@ static int avc_update_node(struct selinux_avc *avc,
 	/*
 	 * If we are in a non-blocking code path, e.g. VFS RCU walk,
 	 * then we must not add permissions to a cache entry
-	 * because we cannot safely audit the denial.  Otherwise,
+	 * because we will not audit the denial.  Otherwise,
 	 * during the subsequent blocking retry (e.g. VFS ref walk), we
 	 * will find the permissions already granted in the cache entry
 	 * and won't audit anything at all, leading to silent denials in
 	 * permissive mode that only appear when in enforcing mode.
 	 *
-	 * See the corresponding handling in slow_avc_audit(), and the
-	 * logic in selinux_inode_follow_link and selinux_inode_permission
-	 * for the VFS MAY_NOT_BLOCK flag, which is transliterated into
-	 * AVC_NONBLOCKING for avc_has_perm_noaudit().
+	 * See the corresponding handling of MAY_NOT_BLOCK in avc_audit()
+	 * and selinux_inode_permission().
 	 */
 	if (flags & AVC_NONBLOCKING)
 		return 0;
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 3eaa3b419463..fd34e25c016f 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3015,8 +3015,7 @@ static int selinux_inode_follow_link(struct dentry *dentry, struct inode *inode,
 
 static noinline int audit_inode_permission(struct inode *inode,
 					   u32 perms, u32 audited, u32 denied,
-					   int result,
-					   unsigned flags)
+					   int result)
 {
 	struct common_audit_data ad;
 	struct inode_security_struct *isec = selinux_inode(inode);
@@ -3027,7 +3026,7 @@ static noinline int audit_inode_permission(struct inode *inode,
 
 	rc = slow_avc_audit(&selinux_state,
 			    current_sid(), isec->sid, isec->sclass, perms,
-			    audited, denied, result, &ad, flags);
+			    audited, denied, result, &ad);
 	if (rc)
 		return rc;
 	return 0;
@@ -3074,7 +3073,11 @@ static int selinux_inode_permission(struct inode *inode, int mask)
 	if (likely(!audited))
 		return rc;
 
-	rc2 = audit_inode_permission(inode, perms, audited, denied, rc, flags);
+	/* fall back to ref-walk if we have to generate audit */
+	if (flags & MAY_NOT_BLOCK)
+		return -ECHILD;
+
+	rc2 = audit_inode_permission(inode, perms, audited, denied, rc);
 	if (rc2)
 		return rc2;
 	return rc;
diff --git a/security/selinux/include/avc.h b/security/selinux/include/avc.h
index 74ea50977c20..cf4cc3ef959b 100644
--- a/security/selinux/include/avc.h
+++ b/security/selinux/include/avc.h
@@ -100,8 +100,7 @@ static inline u32 avc_audit_required(u32 requested,
 int slow_avc_audit(struct selinux_state *state,
 		   u32 ssid, u32 tsid, u16 tclass,
 		   u32 requested, u32 audited, u32 denied, int result,
-		   struct common_audit_data *a,
-		   unsigned flags);
+		   struct common_audit_data *a);
 
 /**
  * avc_audit - Audit the granting or denial of permissions.
@@ -135,9 +134,12 @@ static inline int avc_audit(struct selinux_state *state,
 	audited = avc_audit_required(requested, avd, result, 0, &denied);
 	if (likely(!audited))
 		return 0;
+	/* fall back to ref-walk if we have to generate audit */
+	if (flags & MAY_NOT_BLOCK)
+		return -ECHILD;
 	return slow_avc_audit(state, ssid, tsid, tclass,
 			      requested, audited, denied, result,
-			      a, flags);
+			      a);
 }
 
 #define AVC_STRICT 1 /* Ignore permissive mode. */
-- 
2.23.0

Re: [PATCH 2/2] selinux: fall back to ref-walk if audit is required

[Paul Moore]

On Fri, Nov 22, 2019 at 12:23 PM Stephen Smalley <sds@tycho.nsa.gov> wrote:
> commit bda0be7ad994 ("security: make inode_follow_link RCU-walk aware")
> passed down the rcu flag to the SELinux AVC, but failed to adjust the
> test in slow_avc_audit() to also return -ECHILD on LSM_AUDIT_DATA_DENTRY.
> Previously, we only returned -ECHILD if generating an audit record with
> LSM_AUDIT_DATA_INODE since this was only relevant from inode_permission.
> Move the handling of MAY_NOT_BLOCK to avc_audit() and its inlined
> equivalent in selinux_inode_permission() immediately after we determine
> that audit is required, and always fall back to ref-walk in this case.
>
> Fixes: bda0be7ad994 ("security: make inode_follow_link RCU-walk aware")
> Reported-by: Will Deacon <will@kernel.org>
> Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
> Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
> ---
>  security/selinux/avc.c         | 24 +++++-------------------
>  security/selinux/hooks.c       | 11 +++++++----
>  security/selinux/include/avc.h |  8 +++++---
>  3 files changed, 17 insertions(+), 26 deletions(-)

Also merged into selinux/next, thanks.

-- 
paul moore
www.paul-moore.com

Re: [PATCH 1/2] selinux: revert "stop passing MAY_NOT_BLOCK to the AVC upon follow_link"

[Paul Moore]

On Fri, Nov 22, 2019 at 12:23 PM Stephen Smalley <sds@tycho.nsa.gov> wrote:
> This reverts commit e46e01eebbbc ("selinux: stop passing MAY_NOT_BLOCK
> to the AVC upon follow_link"). The correct fix is to instead fall
> back to ref-walk if audit is required irrespective of the specific
> audit data type.  This is done in the next commit.
>
> Fixes: e46e01eebbbc ("selinux: stop passing MAY_NOT_BLOCK to the AVC upon follow_link")
> Reported-by: Will Deacon <will@kernel.org>
> Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
> ---
>  security/selinux/avc.c         | 24 ++++++++++++++++++++++--
>  security/selinux/hooks.c       |  5 +++--
>  security/selinux/include/avc.h |  5 +++++
>  3 files changed, 30 insertions(+), 4 deletions(-)

Merged into selinux/next, thanks.

-- 
paul moore
www.paul-moore.com